Desulfurization of hot fuel gas is currently the subject of extensive research, primarily because it could lead to thermally efficient power generation in coal-based, combined-cycle systems. Hot-gas desulfurization also has advantages for coal-based direct reduction of iron ore. The use of calcined dolomite has been suggested for desulfurization of hot reducing gases (cf. U.S. Pat. Nos. 3,276,203, 3,307,350 and 3,853,538). While dolomite is an effective gas-desulfurizing agent, the most commonly proposed method of regenerating dolomite, reacting with CO.sub.2 and H.sub.2 O under slightly reducing conditions at pressures greater than about 50 psig and temperatures preferably about 1000.degree.-1200.degree. F. to liberate H.sub.2 S, does not achieve complete regeneration of the dolomite. Furthermore, continuous use of dolomite for gas desulfurization followed by regeneration results in successively less efficient regeneration until, after about 10 cycles, the dolomite has only about 10 to 20 percent of its original desulfurizing capacity remaining. Furthermore, because the spent dolomite contains appreciable non-regenerated calcium sulfide, it must undergo expensive and complex treatment to bring it to a state suitable for disposal without causing pollution of the air and groundwater. When dolomite is calcined after having been regenerated by the above suggested process, some of the residual sulfur in the dolomite can be released, which requires difficult treatment to bring the stack gas to a condition suitable for venting to the atmosphere.
The use of manganese carbonate and oxide ores have been suggested and tried in high temperature removal of sulfur compounds from coke gas. See. N.Y. Buchukuri et al., "The Use of Manganese Carbonate and Oxide Ores in High Temperature Removal of Sulfur Compounds from Coke Gas", Bulletin of Academy of Sciences of the Georgian SSR, Vol. 62, No. 2, 1971. However, the system was not believed to be practical due to the slow rate of reaction as well as the incomplete reaction observed between manganese oxide ore and hot reducing gases containing H.sub.2 S.